(1) Field of the Invention
The present invention relates to novel polyolefin compositions particularly containing significant amounts of elastomers (plasticizers) comprising polybutene-1, a polyolefin other than polybutene-1, a lubricant additive comprising optionally an unsaturated fatty acid ester which acts to reduce surface friction to improve scratch resistance in the molded article, optionally a nanocomposite filler to aid in material stability under temperature changes, optionally a nucleating agent to promote crystallinity and surface hardness, a UV stabilizing package for protection against surface degradation and color change as a result of exposure to ultraviolet light during outdoor exposure, and a coupling agent which links the compositions together. In particular, the present invention relates to polyolefin compositions comprising polypropylene, polybutene-1, a thermoplastic elastomer, the coupling agent and the surface modifiers. The polyolefin compositions are used with color pigments to produce molded articles with a surface finish which has an appearance of clear-coated paint film.
(2) Description of Related Art
Crystalline polypropylene polymers are well known in the prior art. Isotactic, syndiotactic and atactic forms are described in U.S. Pat. No. 6,300,419 to Sehanobish et al. It can be a homopolymer or a copolymer with another olefinic polymer.
Crystalline polybutene-1 and blends with polypropylene are described in U.S. Pat. Nos. 4,727,112 and 4,727,113 to Kohyama et al; 4,886,849 to Hwo et al. These blends have good physical properties.
The use of intercalated and exfoliated layered nanocomposites in polymers to increase strength and heat resistance is well known to those skilled in the art. Illustrative are U.S. Pat. Nos. 4,889,885 to Usuki et al; 5,993,769; 6,261,640; 5,866,645 to Pinnavaia et al; 6,242,500 to Lan et al; 6,228,903 to Beall et al.; 6,057,396 to Lan et al.; 6,287,634; 5,698,624; 5,578,672; 5,552,469 to Beall et al; 6,271,298 to Powell et al; and 6,121,361; 5,973,053; 6,103,817 to Usuki et al; and 6,126,734 to Beall et al. 6,365,661 to Fischer et al; 5,962,553 to Ellsworth; 5,952,095 to Beall et al; 5,952,093 to Nichols; 5,747,560 to Christian. All of the above referenced patents are incorporated herein by reference in their entireties.
U.S. Pat. No. 6,017,989 to Malm et al describes polyolefins modified by an elastomer (plasticizer) which with pigments are used in automotive molded products. The combination in an unpigmented polymer has a haze level of less than 50% as measured by ASTM D-1003-95. Special effect pigments, whether metallic or pearlescent, are described as being particularly suitable for these polyolefin compositions. U.S. Pat. No. 6,753,373 to Winowiecki, published Application No. 2004/0229983 to Winowiecki, and published Application No. 20040229977 to Watson et al filed Nov. 13, 2003 which are incorporated herein in their entirety in reference, disclose similar low haze compositions. The problem is that, given the low haze requirements (less than 50%) to promote colorability and appearance, these compositions have physical properties which make them less than desirable in automotive applications, such as, limited impact performance and limited scratch and mar resistance.
The problem in the use of elastomers to improve the physical properties is twofold. First, the compositions lose strength because of the elastomer and second, the elastomer contributes to a softer surface, which is thus more easily scratchable. In addition, the use of elastomer to make the part non-brittle at temperatures ranging down to −40° C. increases the haze level above 50%, as required in prior inventions. This requirement greatly limits the usefulness of the compositions for many applications in the automotive industry and elsewhere where cold temperature requirements and other physical properties such as scratch resistance and material shrinkage control require use of impact modifiers and other additives.